It is known that hydraulic actuators are employed in various applications utilizing a source of a pressurized hydraulic fluid, for example, as in friction clutch assemblies and hydraulic brake systems. Also, it is common to create the hydraulic pressure to drive the hydraulic actuators with an electric motor, while utilizing a motor driven screw shaft, a non-rotatable nut threaded to the screw shaft, and a hydraulic piston slidably mounted within a hydraulic cylinder and fixed to the nut.
When the electric motor is actuated, the rotary motion of the screw shaft is transmitted to the nut that linearly travels along the screw shaft. Since the piston is fixed to the nut, it also moves along the screw shaft, thus generating a desired hydraulic pressure which translates to torque from the hydraulic piston applying a clamping force on a friction clutch, as taught in U.S. Pat. No. 8,118,571 to Krisher, which is incorporated herein by referenced.
Specifically, Krisher teaches that the torque capacity of a clutch pack is proportional to the hydraulic fluid pressure applied to a second piston, along the screw shaft. A small amount of torque generated by the electric motor can, therefore, result in a significant amount of force on the second piston. Torque amplification is realized by the lead of the motor drive screw, while force amplification is realized by the ratio of a surface area of the piston head of the first piston to a surface area of the second piston.
Although conventional hydraulic actuators have in the past adequately controlled the transfer of torque from a driveshaft to a vehicle rear wheel, it would be advantageous to have actuators that possess faster response times to control the transfer of torque to a vehicle rear wheel, while providing large travel distances to minimize disengage drag torque. Also, it would be a benefit to detect the position of initial clutch engagement and to compensate for mechanical wear due to friction, malfunction, and/or mis-assembly within a differential and its associated parts.